[alkaloid]

I like how most of the comments insult you and tell you to educate yourself, rather than answering a fair question about immutable and immediately-recognizable characteristics.

[kayodelycaon]

At the time I'm writing this, there are exactly two comments (now three) on this thread that aren't an attempt to give an answer.

It's best to read things in good faith. On the whole, people on HN do try to be helpful.